Lightened flywall...pros? cons?

Phate

Phate

Phate

Caporegime
Joined
1 Nov 2003
Posts
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Location
Lisbon, Portugal
Hi all,

Was chatting today to another MG nut...basically in a few days the car is going to be in a prime position to fit one as the gearbox and clutch is being replaced.

The original weighs 17kgs and the lighter one is considerably less.

The pros and cons from what I can see are:

Pros - Engine is more revvy, better throttle response
Cons - Loss of torque

Not sure what it does to MPG? anyone got any ideas? (not that that is a major issue anyway)

Anyone else know the pros and cons? A more revvy response is sounding tempting.

Thanks,
Jake
 
Basically you are making the engine able to spin up faster and slow down faster, so as you say the engine will rev much more freely, up and down.

I think they can make the idle slightly lumpy, no clues on mpg though.
 
As said, it revs more freely, cant say I noticed any loss of torque but then with 350ft/lb theres plenty anyway. So long as you dont go too light there isnt any cons
 
Bear said:
As said, it revs more freely, cant say I noticed any loss of torque but then with 350ft/lb theres plenty anyway. So long as you dont go too light there isnt any cons
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Hmm cool :)

Well I'm not sure what my torque is right now, its been improved with other mods and it'll be done in the remap in a few weeks time, but that was my main concern.

Think I may go for it :)
 
You get faster acceleration and harder engine braking.
Theoretically, you should get better mpg because there is less weight and therefor the engine does less work. But in practice its much harder to maintain a constant speed when cruising so you will be feathering the accelerator more to try and keep it steady which means less mpg.
(FYI I'v never used a lightened flywheel - this is just what i've heard/read about them)
 
neil-ste said:
Torque is just a force the engine generates, how can fitting a lightened flywheel lower the amount it produces?
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I have heard people say that, i don't understand either. I wonder if maybe its because the engine goes through the rev range faster so spends less time than before at peak torque? :confused:

edit: Ok, so i read the link above and i'm even more confused than before :D
 
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It won't produce any more power, not a jot in real terms but it should give a slightly sharper throttle response which is nice and should allow more power (though I suspect you wont notice it) to go to the rear wheels. It can make the tick over somewhat more lumpy however. Having driven a GT3 with normal and single mass flywheel the difference was all in the throttle response not in the performance and even then it wasn't huge. Its not something of any real benefit on a run of the mill motor in my opinion but as with all these things its a subjective call. It's a hi-fi speaker cable thingy.
 
I can't quite imagine how it can make the engine rev up faster either unless you're out of gear all the time. The way I see it the only way it will rev up quicker is if it's making more power..?
 
it also has some odd effects in acting as a overall engine mass while running.

i cant remember the exact figures but i think it was something like if you have 1kg took off the flywheel the effect is akin to having a 20kg lighter engine.

il see if i can find my notes.
 
Clarkey said:
I can't quite imagine how it can make the engine rev up faster either unless you're out of gear all the time. The way I see it the only way it will rev up quicker is if it's making more power..?
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It doesnt have a big weight to spin around? :confused:
 
A lighter flywheel won't reduce the amount of torque the engine produces, but as said above it will reduce the amount of available torque (moment of inertia) in the drive train, so engine breaking etc will be more pronounced
 
OllyM said:
Isn't this a bit overkill? :confused:
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My thoughts. On a fully-fledged track car yes - you need to be able to get the revs up as quickly as possible. On any road-going car, no , you don't need it. I was actually advised against this, by the guy who stood to make some money fitting one.


M
 
A few people I know on forums say after fitting them the engine is definately more free revving but pulling off and town traffic can be a pain as you have to rev more to get moving. I'm all for a smooth drive so I personally wouldn't fit one.
 
lighter flywheels dont reduce torque, its a myth.

Engine will rev more freely, you may lose some top end but nothing that would make a noticeable difference.
 
Clarkey said:
I can't quite imagine how it can make the engine rev up faster either unless you're out of gear all the time. The way I see it the only way it will rev up quicker is if it's making more power..?
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A flywheel is an energy storage device. To accelerate it up to a given speed in a given time requires a fixed amount of power. Reduce the weight of the flywheel (or more accuracy reduce it's moment of inertia), and for the same power input you reach the same speed more quickly.

A lightened flyweel can give worthwhile performance improvements in lower gears, where the flywheel is a significant fraction of the total load on the engine. The advantage drops off in higher gears, since the load of the mass of the car swamps the effect of the flywheel.

One thing to bare in mind; a badly modified cast flywheel is basically a fragmentation grenade. The damage they can do if they explode at high RPM is frightening, the parts will slice through bellhousings and thin steel body panels like butter. A billet steel item should always be used if you want to save a significant amount of weight.
 
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